rear wheel problem dex210

[wasdebeer]

Hey, I'm new here so I guess a quick introduction is in order, I'm quite new to the rc world had a whole run of crappy toy rc cars as a kid but always wanted the real thing so I ended up getting a good one a short while ago. Now I've been slowly getting into it I don't have any body around with some experience with these things to help me out so it's been a steep curve. Now a problem arose that I just can't figure out so I decided to try and find some help here.

The problem at hand, I noticed today that my right rear wheel had quite a bit of play special compared to the left one, inspecting it I noticed the driveshaft on the right side is sliding with a cap coming out of the inside of the axl, it moves furthest when the rear shocks are compressed and the axl is straight moved out all the way it goes it even blocks the arm from coming down fully, Ive added a picture to show the axl slide out of place, I have no idea what's causing this let alone how to fix it. I'm sorry if this is a obvious question but I am a complete noob, willing to learn to ! Much appreciated if I could get some help with this.